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Period: to
Atomic Model Timespan
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Dalton's Theory
In 1803, John Dalton's atomic theory was adopted
His theory included that
-Elements are made of extremely small particles called atoms
-Atoms of a given element are equal in size, mass, and other properties. Atoms of different elements are different in size, mass, and other properties
-Atoms can't be subdivided, created, or destroyed
-Atoms combine in whole number ratios to make compounds
-In chemical reactions atoms are combined, separated or rearranged -
Discovery of the Electron
J. J. Thomson discovered the electron in 1897 -
Plum Pudding Atomic Model
J. J. Thomson proposed that the atom was negatively charged electrons floating in a possitively charged mass. -
Gold Foil Experiment
Ernest Rutherford did an experiment of shooting particles through a very thin sheet of gold foil, expecting them to be slightly deflected by the electrons in the atom, validating Thomson's atomic theory. But his experiment showed that the Thomson model was wrong and that the atom was mostly empty space with a solid mass (the nucleus) in the middle. -
Rutherford's Atomic Model
Rutherford proposed that an atom was mostly empty space with a concentrated nucleus in the middle and electrons orbiting around it in unfixed orbits -
Bohr Atomic Model
Niels Bohr expanded on Rutherford's model, describing how electrons circled the nucleus in fixed paths called orbitals and how they could change orbitals with changes in energy, but could not orbit in between orbitals. -
Heisenberg Uncertainty principle
Werner Heisenberg developed matrix mechanics to describe how you could never tell exactly where an electron was or how fast it was going. -
Electron Cloud Atomic Model
The current model of the atom is the electron cloud model. It was adopted in 1927. It takes into accound the Heisenberg uncertainty principle because it shows how you can never be sure where an electron will be.
